Various colorants and dyes have been used to authenticate the composition and/or source of fluids and plastic articles. In some cases, it is preferable to use a marker or tag that is not detectable by the human eye so as to avoid interference with colored materials or to avoid detection of the additive. In such cases, it may be desirable to use marker compounds containing fluorophores that fluoresce or emit light in the ultraviolet or infrared region after excitation with an appropriate light source. For instance, U.S. Pat. Nos. 4,303,701 and 4,329,378 disclose methods for marking plastic lenses by impregnating them with fluorescent materials that do not respond to sunlight or normal visible light. Luttermann et al., in U.S. Pat. No. 5,201,921 teach a process for identifying polyolefin plastics using lipophilic fluorescent dyes in concentrations suitable to minimize color distortions.
Markers are also becoming particularly important for protecting brand integrity for consumers. Such markers must be readily detectable at relatively low concentrations in the product. In the petroleum industry, markers are also useful for ensuring compliance with governmental regulations. For example, products such as diesel fuels, gasoline and heating oils often contain visible dyes or colorless fluorescent compounds that identify the intended use, tax status, or brand name of the product. Such markers are well known to those skilled in the art.
In addition, petroleum product markers must also fulfill other criteria such as being:                (1) soluble in hydrocarbon solvents;        (2) resistant to leaching from the petroleum product by water or water that is strongly acidic or basic;        (3) relatively chemically inert so as to avoid loss of color or fluorescence when in contact with other petroleum additives or water; and        (4) free from interference from naturally occurring compounds already present in the petroleum product.        
A number of artisans have attempted to provide acceptable fluorescent markers for use in the petroleum industry. For example, Smith, in U.S. Pat. No 5,498,808, teaches the use of colorless fluorescent petroleum markers which are based on esterified derivatives of xanthene compounds such as fluorescein. One drawback to the markers of Smith is that fuels containing these markers must be treated with alkaline developing solutions to generate the visibly fluorescent chromophore. Other markers such as the phthalocyanine and naphthalocyanine dyes, disclosed in U.S. Pat. Nos. 5,804,447, 5,998,211 and 6,312,958, can be detected directly by their fluorescence in the near infrared (IR) region between 600 to 1,200 nm where naturally occurring components in the petroleum product will not interfere.
Carbamates or urethanes prepared with aromatic isocyanates are known to fluoresce in the ultraviolet region between 300 and 400 nm depending upon the substitution pattern of the isocyanate, solvent, and the alcohol used. Because petroleum compounds typically exhibit considerable background fluorescence at these wavelengths, urethanes have heretofore tended to be excluded from consideration as markers.
U.S. Pat. Nos. 3,844,965 and 4,897,087 disclose lubricating oil additives and ashless fuel detergents or dispersants which are said to be the reaction products of a polyether polyol and an aliphatic hydrocarbyl amine or polyamine with a polyisocyanate (i.e., polyether urethaneureas). Polyether urethane polyamines prepared from hydroxyalkylated polyamines, a polyisocyanate, and a polyether can be used as fuel additives with enhanced oxidative stability as taught by Blain et al. in U.S. Pat No. 5,057,122. However no mention is made in any of these patents about the use of these compounds as fluorescent markers and no methods of enhancing their fluorescent response is discussed.
Polyether polyurethanes without active hydrogens have been used as plasticizers in U.S. Pat. Nos. 4,824,888, 5,525,654, and 6,403,702. These compounds are essentially diurethanes prepared by:                1) reaction of difunctional polypropylene glycol with a monoisocyanate or        2) reaction of a monofunctional monalkyl ether of polypropylene glycol with a diisocyanate.        
Pantone et al., in U.S. Pat. 6,384,130, disclose another class of plasticizers that are the reaction products of an isocyanate-terminated prepolymer and a monofunctional alcohol. These compounds contain more than two urethane groups and the prepolymers may have a functionality greater than 2.0. The polyethers disclosed by Pantone et al. to make the polyurethanes do not contain fluorophores.
Reactive dyestuffs or colorants for plastics based on alkoxylated chromophores such as azo, triphenylmethane, and anthraquinone derivatives are disclosed in U.S. Pat. Nos. 4,284,729 and 4,846,846. The polyether derivatives provide non-migrating visible color to polyurethane articles by chemically reacting with isocyanates in the blend to become part of the polymer network. Again, no mention is made in any of these patents about the use of these compounds as fluorescent markers and no methods of enhancing or controlling their fluorescent response is discussed.
Thus, a need continues to exist in the art for colorless markers. It would be desirable if such markers had molecular structures that can be readily modified to provide fluorescence in the ultraviolet, visible, or near infrared (IR) region of the electromagnetic spectrum.